Sandpaper



United States Patent SANDPAPER John F. Twombly, Aiken, S. C., assignor, by mesne assignments, to Norton Company, Worcester, Mass, a corporation of Massachusetts No Drawing. Application June 29, 195%, Serial No. 440,293

20 Claims. (Cl. 51-295) This application is a continuation-in-part of my application Serial No. 228,123,, filed May 24, 1951.

This invention relates to improved abrasive fabrics generically called sandpaper and to a new technique in sandg or abrading articles which have been coated with lacquers, enamelsand the like.

In the manufacture offurniture and similar articles from wood the latter is usually selected for its beauty of grain pattern rather than strength. It is common to. enhance the beauty of the wood by means of fillers, sealers andclear protective finishes. Sometimes the wood is dyed with aqueous acid dyes followed'by a wash coat which usually is'shellacor lacquer sealer reduced to about 5% solids; Compositions of this type are disclosed in U. S. Patent No. 2,293,558 for increasing the adhesion of subsequent coats. The Wood'is later filled and sealed. The sealing-coat is then sanded when dry and the final composition'i'sapplied. i

The present invention is concerned primarily with the treatment of the sandpaper used at this stage of the preparation of the wood; The termsandpaper is intended to include fabrics such as paper or cloth coated With animal glues or synthetic adhesives in which have been embedded abrasive gritsei'ther ina closed or open pattern. The grits, although called sand, are usually made of improved abrasives such as artificially fused aluminum oxide, silicon carbide or natural abrasive grains, such as flint, garnet, emeryandthe like; The first steps in the preparation of the abrasive'fabric including the type of adhesive and grits do not specifical y form a part of the present invention, and theymay be of any known type or combination of g'rjit,l'adhesive, and fabri'c'or web subst rate.

When: thewoodhas been filled and sealed, it is sanded; Conventional abrasive-fabrics, however, areoften clogged in: a relatively short time by the sealer composition which becomes gummy under heat. Many ex'pedientshave been resorted to-toovercome this clogging, usually by inlcorporating a so-called sanding aid in'the sealer composition. Such- 'aid's invariably detract from the desirable properties of the; sealer by decreasing its st'reng'th'and' intercoat adhesionand increasing brittleness;

It is: an object of the present invention to'provide an abrasive sheet which exhibits excellent resistance to cloggingand gumming; Another object is the provision of such anabrasive sheet which permitsthe omission of sanding aids in: the preliminary coats used to prepare'the Woodi'for the finaljsurface film. Other objects will be apparentfa's the-description-of the invention proceeds.

These objects: are accomplished by applying to the abrasive fabric a: metallic soap such as the stearates or palrnitates'of zinc or those; of aluminum; barium, calciunr, lead; magnesium" and strontium in an amount ranginglfrom- 0.1 to about milligramsper square inch of: abrasive surface. In; the preferred embodiment of the-invention, the abrasive sheet is coated with zinc-stearate inithe 'amount ranging from 0:5 to -25'milligramsper square inch of the abrasive area. The-metallic soap may be: applied: dry by brushing, on preferably applied in. the

fprmaofra. dispersions of thezsoap-ini a: volatilezliquich by 2,768,886 Patented Oct. 30, 1956 2 spraying. The volatile liquid may consist of esters, alcohols, ketones, hydrocarbons and mixtures thereof. Even water may be used as a dispersion medium for these Waterinsoluble metallic soaps. The dispersion medium is so selected that it does not'have a deleterious effect on the adhesive used to bond the grit to the substrate and can be easily volatilized. The dispersion medium should be one which is effective to disperse the coating material without dissolving a substantial part thereof. The dispersion can also be applied by any con: ventional method, such as dipping, roller coating, brush ing and so forth as long as the required amount is applied to the surface of the abrasive fabric. The following composition is illustrative ofa suitable dispersion for spray coating:

ZINC'STEARATE DISPERSION The first portion was charged into a pebblemill and ground with pebbles for two hours. Thereafter the secend portion was added to the charge in the mill to facilitate removal ofthe batch from the mill.

The product was reduced to spraying viscosity with lacquer thinner and applied to the abrasive. In place of the lacquer thinner, cheaper diluent's such as gasoline, M. &, P.- naphtha, toluene,- xylene; benzol and similar hydrocarbons may be used. Liquids of this type may also replace the butyl acetate and alcohols in like proportions in the example. The coating weight wasa'djusted by varying the solids content of the dispersion and by the" number 'of'coats applied? For experimental test purposes the dispersion wa'ssp'rayed' on'pieces of sandpaper measuring 2 /2 x 4""; The zincstea'rate'was present as anunfused surface coating of small; solid particles. When dry; the sheet was weighed to determine the-coating Weight and' then cut in half and adhesively mounted at the small end of" a" lead block having the dimensions 6- x 4 x 1". This block Weighed approximately ten pounds. H

In testing, the block with. its abrasive face in contact with: a: previouslyprepared filrnof coating composition was pushed back and forth over the said film with'1'2 inch strokes at a frequency of 2 seconds per stroke; The number of strokes required to cut through agivenfilm thickness was then determined as a measure of cutting rate.

The following; lacquer vehicle compositionv represents atypical sealer ,andwas used to evaluate the. cutting characteristics ofcoated sandpaper. Normally the comaposition includes: 1.3- parts of zinc" stearate asa sanding aid, but this' is-omitt'ed when thema'terial is used for testing; theefiiciency of the: coated sandpaper.

. Parts Cellulose nitrate 11.7 Blowncastor oil' 614 Dibutyl phthalate; Q. a 056" Lacquer solvent. 2 2.9 Alcoholic diluents 1'95 Hydrocarbon diluents. 37 6 The transparency of the above lacquer vehicle makes it difficult to observe the cut-through point and therefore to make the observation easier, the composition was tinted with 'a trace of red dye.

The above composition was spray coated on 12 x 14" glass panels to yield dry films of about 0.8 to 1.0 mil thickness. These panels were subjected to various drying conditions and after film thickness was ascertained, the films were subjected to abrading action with uncoated sandpaper and with sandpaper coated with various determined amounts of Zinc stearate.

While the invention is illustrated in Examples I and II by the use of zinc stearate, it is to be understood that substantially comparable results are obtained when the other stearates or palmitates mentioned above or mixtures thereof are used in the examples in like amount. The following results show the effect of lubricating the surface of #220 6/0 silicon carbide finishing paper when used on the aforementioned composition dried overnight to a film thickness of 0.8 mil.

Example I Mgs. of zinc stearate Sanding per square inch: strokes 50 0.5 17 1 15 2 14 4 11 6 11 9 13 The uncoated sandpaper sanded through in 50 strokes, but the paper was badly clogged and excessive rolling was in evidence.

Example II The same film thickness of clear lacquer dried for one hour showed similar results which indicated an optimum concentration of zinc stearate.

The omission of zinc stearate cause rolling and prohibitive clogging. Although 0.5 mg. significantly improved the sanding properties, rolling and clogging were present to a minor degree.

' Similar tests were made with 2/0, 3/0, 5/0, 6/0, 9/0 and other grades of silicon carbide or aluminum oxide abrasive fabrics with comparable reduction in the number of sanding strokes to wear through the coating.

Improved sanding rates are observed when the wood is sealed with a large variety of compositions and the invention is not limited to any particular sealer coat. An indirect result of the invention, however, is that sanding sealers, particularly those used in furniture finishing may be formulated on a higher quality basis by decreasing or entirely eliminating the amount of sanding aid incorporated therein. When these aids are eliminated or decreased to a large extent, the intercoat adhesion and mar resistance is greatly improved. The beauty of the wood is also further enhanced by the improved clarity and transparency of the finish resulting from the elimination of the sanding aid which invariably increases the opacity of the coat in which it is incorporated.

Zinc stearate, suitable for use in my invention, is obtainable commercially in relatively pure form, for example, about 99% pure as calculated from the metallic zinc content, and about 96% pure as calculated from the stearic acid content, although zinc stearate of such high purity is not required. a

When relatively pure zinc stearate is applied to the abrasive side of coated abrasives by the methods disclosed herein, and in particular by coating with a dispersion of zinc stearate in water or in volatile organic liquids which are efiective to disperse zinc stearate without dissolving a substantial part thereof, as disclosed herein, solid unfused surface coatings are formed when the volatile liquid is evaporated.

By the term solid I mean that the coatings are dry, non-flowable and non-plastic under ordinary atmospheric conditions. By the term unfused I mean that the coatings are not of the type normally obtained by coating, according to the hot melt method, as understood in the art, or by heating high enough to fuse a dried coating applied as disclosed herein.

Relatively pure zinc stearate, when applied to the abrasive surface of coated abrasives by my dispersion methods, as taught herein, forms unfused solid surface coatings having physical and chemical properties useful in the preferred form of my invention.

I have used, by my dispersion methods, a number of other materials, such as calcium stearate, lead stearate, cadmium stearate, chromic stearate, aluminum stearate, barium stearate, magnesium stearate, strontium stearate, Zinc palmitate, lead palmitate, zinc undecylenate, calcium myristate and methylene distearamide, and obtained unfused solid surface coatings on the abrasive side of coated abrasives having similar physical and chemical properties to those obtained with zinc stearate, as well as giving similar results in sanding to those obtained with coatings of zinc stearate as described herein.

I have also found the palmitates of aluminum, barium, calcium, magnesium and strontium to be useful.

Likewise, coatings formed from dispersions of mixtures, of the various materials found useful in my invention when used alone, are, of course, satisfactory, provided they have similar physical and chemical properties to those of my zinc stearate coatings applied similarly and in the same amount.

In many experiments that I have run with the various materials above recited (e. g., the metallic palmitates, stearates, methylene distearamide, etc.), I have not found any case in which an unfused solid surface coating, formed on coated abrasives with other materials, as described herein for zinc stearate, and having similar physical and chemical properties to those of my unfused surface coatings of zinc stearate, did not give similar results in sanding tests to those described herein for my zinc stearate coatings.

It is well known to those skilled in the art that some commercial organic acids available, such as for example, stearic acid and palmitic acid, are very impure and contain large amounts of such materials as oleic acid. In some cases, stearates and palmitates formed from very impure acids are not desirable in carrying out my invention, in which I form unfused surface coatings on coated abrasives having physical and chemical properties similar to those of my zinc stearate coatings, although purer forms of the stearates and palmitates of the same metals may be highly satisfactory for my use.

No theory is advanced for the action of the metallic soaps in decreasing the clogging and gumming of the abrasive fabric. Many materials have been used to accomplish this result, such as greases, waxes, oils, talc, graphite and the like, but they all have disadvantages either in low efliciency or in adversely affecting the wood bystaining, discoloring, decreasing transparency or failing to prevent gumming.

It is apparent that many widely different embodiments of the present invention may be made without departing from the spirit and scope thereof, and therefore, it is. not intended to be limited, except as indicated in the append dclaixn I claim; 7

1- An a s ve heet ompr singa fabric bas n adh i a ach d ther o aving abr sive gri embedd e n u s d surface c ating of all, so i particles consisting essentially of at least one material selected from the group consisting of zinc stearate, calcium stearate, lead stearate, "cadmium stearate, chromic stearate, barium stearate, magnesium stearate, strontium stearate, zinc palmitate, lead palmitate, zinc undecylenate, calcium myristate, aluminum stearate, barium palmitate, calcium palmitate, magnesium palmitate, strontium palmitate, aluminum palmitate, and methylene distearamide on the abrasive side of said sheet in an amount of 0.1 to 50 milligrams per square inch of surface area.

2. The article of claim 1, in which the unfused solid surface coating is present in amount between 0.5 and 25 milligrams per square inch of surface area.

3. An abrasive sheet comprising a fabric base, an adhesive attached thereto having abrasive grits embedded therein, and an unfused surface coating of small, solid particles of zinc stearate on the abrasive side of said sheet in an amount of 0.1 to 50 milligrams per square inch of surface area.

4. An abrasive sheet comprising a fabric base, an adhesive attached thereto having abrasive grits embedded therein, and an unfused surface coating of small, solid particles of calcium stearate on the abrasive side of said sheet in an amount of 0.1 to 50 milligrams per square inch of surface area.

5. An abrasive sheet comprising a fabric base, an adhesive attached thereto having abrasive grits embedded therein, and an unfused surface coating of small, solid particles of lead stearate on the abrasive side of said sheet in an amount of 0.1 to 50 milligrams per square inch of surface area.

6. An abrasive sheet comprising a fabric base, an adhesive attached thereto having abrasive grits embedded therein, and an unfused surface coating of small, solid particles of zinc palmitate on the abrasive side of said sheet in an amount of 0.1 to 50 milligrams per square inch of surface area.

7. An abrasive sheet comprising a fabric base, an adhesive attached thereto having abrasive grits embedded therein, and an unfused surface coating of small solid particles of methylene distearamide on the abrasive side of said sheet in an amount of 0.1 to 50 milligrams per square inch of surface area.

8. In the process of preparing sheet abrasives wherein a fabric is coated with an adherent adhesive having embedded therein abrasive grains, the improvement which comprises applying to the abrasive side of the said sheet an unfused surface coating of small, solid particles of coating material consisting essentially of at least one maerial selected from the group consisting of zinc stearate, calcium stearate, lead stearate, cadmium stearate, chromic stearate, aluminum stearate, barium stearate, magnesium stearate, strontium stearate, zinc palmitate, lead palmitate, zinc undecylenate, calcium myristate, barium palmitate, calcium palmitate, magnesium palmitate, strontium palmitate, aluminum palmitate, and methylene distearamide, said coating material being applied as a dispersion of solid particles of the coating material in a substantially inert volatile liquid dispersing medium in which said coating material is substantially insoluble, and dried to form said unfused surface coating of small, solid particles, the dispersion being applied in a quantity such that the final product has 0.1 to 50 milligrams of said coating material per square inch of surface area.

9. In the process of preparing sheet abrasives, wherein a fabric is coated with an adherent adhesive having embedded therein abrasive grains, the improvement which comprises applying to the abrasive side of the said sheet a dispersion of undissolved solid particles of zinc stearate final producthas 0.1 to 50 milligrams of zinc stearate per square inch of surface area.

.10. 'In the process of preparing sheet abrasives, wherein a fabric is coated with an adherent adhesive having embedded therein abrasive grains, the improvement which comprises applying to the abrasive side of the said sheet a dispersion of undissolved solid particles of calcium stearate in an inert volatile liquid in which the calcium stearate is substantially insoluble, and drying to form an unfused surface coating of small, solid particles of calcium stearate, the dispersion being applied in a quantity such that the final product has 0.1 to 50 milligrams of calcium stearate per square inch of surface area.

11. In the process of preparing sheet abrasives, wherein a fabric is coated with an adherent adhesive having embedded therein abrasive grains, the improvement which comprises applying to the abrasive side of the said sheet a dispersion of undissolved solid particles of lead stearate in an inert volatile liquid in which the lead stearate is substantially insoluble, and drying to form an unfused surface coating of small, solid particles of lead stearate, the dispersion being applied in a quantity such that the final product has 0.1 to 50 milligrams of lead stearate per square inch of surface area.

12. In the process of preparing sheet abrasives, wherein a fabric is coated with an adherent adhesive having embedded therein abrasive grains, the improvement which comprises applying to the abrasive side of the said sheet a dispersion of undissolved solid particles of zinc palmitate in an inert volatile liquid in which the zinc palmitate is substantially insoluble, and drying to form an unfused surface coating of small, solid particles of zinc palmitate, the dispersion being applied in a quantity such that the final product has 0.1 to 50 milligrams of zinc palmitate per square inch of surface area.

13. In the process of preparing sheet abrasives, wherein a fabric is coated with an adherent adhesive having embedded therein abrasive grains, the improvement which comprises applying to the abrasive side of the said sheet a dispersion of undissolved solid particles of methylene distearamide in an inert volatile liquid in which the methylene distearamide is substantially insoluble, and drying to form an unfused surface coating of small, solid particles of methylene distearamide, the dispersion being applied in a quantity such that the final product has 0.1 to 50 milligrams of methylene distearamide per square inch of surface area.

14. The article of claim 3, in which the zinc stearate is present in amount between 0.5 to 25 milligrams per square inch of abrasive area.

15. The process of claim 9, in which the zinc stearate is applied in the amount of 0.5 to 25 milligrams per square inch of abrasive area.

16. An abrasive sheet comprising a fabric base, an adhesive attached thereto having abrasive grits embedded therein, and an unfused surface coating of small, solid particles consisting essentially of at least one material of the group consisting of zinc stearate, calcium stearate, lead stearate, barium stearate, magnesium stearate, strontium stearate, zinc palmitate, lead palmitate, aluminum stearate, barium palmitate, calcium palmitate, magnesium palmitate, strontium palmitate and aluminum palmitate, on the abrasive side of said sheet in an amount of 0.1 to 50 milligrams per square inch of surface area.

17. The process of claim 8, wherein the volatile liquid consists of at least one hydrocarbon.

18. The process of claim 8, wherein the volatile liquid is organic.

19. The process of claim 8, wherein the volatile liquid is waters 20. The process of claim 8, wherein there is employed a volatile organic liquid dispersion having the following composition:

7 Parts Butyl acetate 53.9 Isopropyl alcohol 8.9 Butyl alcohol 13.6 Zinc stearate References Cited in the file of this patent UNITED STATES PATENTS Hartman Feb. 9, 1932 FOREIGN PATENTS Great Britain Nov. 7, 1929 

1. AN ABRASIVE SHEET COMPRISING A FABRIC BASE, AN ADHESIVE ATTACHED THERETO HAVING ABRASIVE GRITS EMBEDDED THEREIN, AND AN UNFUSED SURFACE COATING OF SMALL, SOLID PARTICLES CONSISTING ESSENTIALLY OF AT LEAST ONE MATERIAL SELECTED FROM THE GROUP CONSISTING OF ZINC STEARATE, CALCIUM STEARATE, LEAD STEARATE, CADMIUM STEARATE, CHROMIC STEARATE, BARIUM STEARATE, MAGNESIUM STEARATE, STRONTIUM STEARATE, ZINC PALMITATE, LEAD PALMITATE, ZINC UNDECYLENATE, CALCIUM MYRISTATE, ALUMINUM STEARATE, BARIUM PALMITATE, CALCIUM PALMITATE, MAGNESIUM PALMITATE, STRONTIUM PALMITATE, ALUMINUM PALMITATE, AND METHYLENE DISTEARAMIDE ON THE ABRASIVE SIDE OF SAID SHEET IN AN AMOUNT OF 0.1 TO 50 MILLIGRAMS PER SQUARE INCH OF SURFACE AREA. 